The monoclonal antibody (Mab) 2F5 is a potent neutralizer of both laboratory strains and primary isolates of most clades of HIV-1, reacting with the largely conserved peptide sequence ELDKWAS (SEQ ID No: 1) of the virus envelope protein gp41, sometimes called the Katinger Epitope (refs. 1 to 7. Throughout this application, various references are referred to in parenthesis to more fully describe the state of the art to which this invention pertains. Full bibliographic information for each citation is found at the end of the specification, immediately preceding the claims. The disclosures of these references are hereby incorporated by reference into the present disclosure). As such, Mab 2F5 is of major interest in the development of an HIV-1 vaccine. Based on studies of immunogenic presentation, the antigenicity of the epitope sequence was concluded to be contingent upon its molecular context (ref. 8).